The present invention relates to a remote monitoring method for a gas turbine installed in a power plant or the like, and particularly to a remote monitoring method and its system capable of preventing the turbine components from being damaged by resonance with combustion oscillations in a turbine.
In a gas turbine operating at a power plant or the like, compressed air from the compressor and gaseous fuel are fed to a combustor and the turbine is driven by combustion gas of a high temperature resulting from combustion in the combustor. Moving vanes are installed around the rotary shaft of the turbine for the compressor and turbine. The moving vanes for the turbine are driven by high temperature combustion gas supplied from the combustor. In the combustor, a fuel nozzle for feeding main fuel and a pilot nozzle for feeding pilot fuel are installed inside a combustor sleeve. Fuel and air discharged from the compressor are mixed and burnt, and combustion gas is fed into the turbine from the tail sleeve of the combustor. In recent years, a gas turbine is designed with consideration given to environmental issues, and efforts have been made to cut down the amount of NOx emission. Especially in the pilot nozzle, for which pre-mixing with air is not performed, diluted fuel gas is used. Use of this diluted fuel gas raises a problem of making combustion in the combustor unstable, pulsating the flow of combustion gas and increasing oscillations associated with the combustion. Similarly, in order to save energy, it is also necessary to raise operating temperature so as to increase efficiency. This requires more fuel to be burnt and makes combustion in the combustor unstable.
Combustion oscillation can be controlled to some extent, for example, by adjusting the air-fuel ratio (A/F ratio), the pilot ratio and the angle of opening of a bypass valve. During initial operations after the gas turbine is installed, it is possible to make adjustment so as to reduce combustion oscillations. As described above, however, in recent designs of gas turbines that are characterized by a reduced amount of NOx emission, higher operating temperatures and improved efficiency, combustion oscillation will restart as the equipment deteriorates after extended operations. In the worst case, parts may be damaged due to resonance with natural frequencies of bolts, nuts and other component parts of the combustor and turbine.
To solve the problems in such a plant as a power plant equipped with a gas turbine, a proposal has been put forward to monitor gas turbine operation parameters via a communications line at a remote monitoring center and to supervise operational conditions. It is possible to consider that the state of the aforementioned combustion oscillation is monitored from the remote monitoring center to ensure that combustion oscillations will not exceed a predetermined level. In order to monitor the state of combustion oscillations at the monitoring center, however, it is necessary to send and monitor a large amount of oscillation data via the communications line with a higher frequency than characteristic frequency of turbine operation.
To send such a large amount of combustion oscillation data, however, only a communications method wherein a telephone line such as ISDN is connected by line switching method can be utilized among the currently used data communications methods. But such a high-speed communications method involves a high communications cost. Thus, a very high cost is required to supervise a gas turbine in the plant built in an overseas country from the domestic monitoring center, and its feasibility is considered very low. As a result, maintenance of a gas turbine characterized by high temperature, high efficiency and low NOx rate has to be provided by a supervisor stationed in the local plant.
In this case, a special skill based on a comparatively long experience is required in order to monitor the state of combustion oscillations and evaluate whether parts will be damaged in advance. It is not easy to find out a skilled engineer to meet such requirements. In practice, it is difficult to have a skilled engineer stationed at a local site, and so an engineer will have to be dispatched after the power plant has been tripped due to damaged parts.
One of the objects of the present invention is to provide a remote monitoring method and system for monitoring the state of combustion oscillations in a turbine combustor from a remote monitoring center. Another object of the present invention is to provide a remote monitoring method and system for preventing parts from being damaged by resonance with turbine combustion oscillation. A further object of the present invention is to provide a remote monitoring method for monitoring from a remote monitoring center a predetermined state which causes the turbine to trip.
To achieve the above objects, the first aspect of the present invention is characterized by monitoring at a remote monitoring center the state of combustion oscillation in the turbine combustor in, for example, a power plant where the turbine is installed. To monitor the state of combustion oscillation, the present invention uses a combination of a low-speed communications mode utilizing the Internet and a high-speed communications mode based on a line switching method such as ISDN. The Internet provides a comparatively low-cost communications means, but it is not suited for a high precision transmission of a large amount of data because of its low speed. The ISDN-based line switching method allows a communications line to be established between the plant and monitoring center to perform data communications. It ensures a high-speed and high-precision transmission of a large amount of data with high degree of security, but the communications cost is not low. According to the present invention, data on combustion oscillation in combustor is separated into two types: first data obtained on a real-time basis and second data consisting of representative values within a predetermined period of time obtained from the first data. During normal operation, the second data is transmitted in a low-speed communications mode of the Internet or the like and monitored at a monitoring center. If any abnormal condition is predicted as a result of monitoring the second data, the first data is transmitted in a high-speed communications mode of ISDN or the like, and combustion oscillation data is monitored in greater details at the monitoring center. If a critical problem is predicted, an instruction is sent to the local site to switch the operation mode over to a low-load operation mode, whenever required.
In a preferred embodiment of the present invention, data on combustion oscillation in combustor is separated into two types: frequency spectrum data (the first data) of oscillation level obtained by Fourier transformation from the oscillation waveform subjected to real-time sampling, and peak value data (the second data) of resonance frequency bands obtained therefrom within a predetermined period of time. During normal operation, the Internet is used to send the peak value data, and when abnormal conditions are found characterized by severe combustion oscillation, ISDN is utilized to send frequency spectrum data. This allows the remote monitoring center to predict the abnormal state of the turbine by monitoring peak value data during normal operation. When a symptom for abnormal conditions is observed, frequency spectrum data received via ISDN is monitored by the center. Immediately before combustion oscillations increase to the extent of damaging turbine component parts, the center issues an instruction to the local site to switch the operation mode over to the low-load operation mode, thereby preventing the turbine parts from being damaged and the plant from tripping.
To achieve the above object, the second aspect of the present invention is characterized in that, in the aforementioned first aspect, a symptom detection computer for detecting the symptom of a critical state is installed in the plant and this computer checks whether a combination of the peak value data and turbine operation parameter values is similar to the past reference data which was obtained when a symptom of the critical state was detected. If a symptom is detected, an alarm is issued to the plant.
Even if the peak value data based on which the symptom for critical state is detected is different, more accurate symptom detection in conformity to the operation state can be performed by checking if a combination of the peak value data and operation parameter values is close to the reference data.